Numerical analysis of extracellular fluid flow and chemical species transport around and within porous bioactive glass

Preparation of a Gradient Biotinylated Polyethylene Surface To Bind Streptavidin−FITC

A novel biotinylated gradient surface was designed to bind a streptavidin-FITC. The gradient polyethylene (PE) surface was prepared by a corona treatment with a power increase along the PE length, and successively, biotinylated gradient PE surface was prepared by the reaction of polyethylenimine (PEI) and biotin. Surface properties of the gradient PE surface changed according to PE length and chemical modification. The biotinylated gradient PE surface provided a continuous gradient of streptavidin-FITC through binding of avidin-biotin. The luminosity of fluorescence that corresponds to a streptavidin-bound FITC on the biotinylated gradient PE surface increased gradually on the surface along the PE length.

High concentrations of bioactive glass material (BioGran) vs. autogenous bone for sinus floor elevation

In this study, high concentrations of bioactive glass (BG) particles were compared with autogenous bone in their capacity to augment maxillary bone when grafted in the human sinus floor using a split mouth design. Three female patients with severe maxillary atrophy underwent bilateral sinus floor elevation and bone grafting using 80-100% BG particles (300-355 microm in size) mixed with 20% to 0% iliac crest bone particles at one (experimental) side, and 100% iliac crest derived bone particles at the other (control) side. A total of 22 bone biopsies was taken at the time of fixture installation; that is, at 4, 6 and 15 months after grafting, and processed for histology and histomorphometry. At the control (autogenous bone) sides, trabecular bone amounted to 39% of the biopsy volume in the graft (site) at 4 months, almost 41% at 6 months, and 42% at 15 months. This bone contained viable osteocytes and was mostly of mature, lamellar type. At the experimental (BG particles) sides, the graft consisted of 27% of mostly woven (and some lamellar) bone at 4 months, 36% (woven and lamellar) bone at 6 months, and 39% (mainly lamellar) bone at 15 months. The grafted BG particles started to excavate at 4 months and their centers gradually filled with bone tissue. As a consequence, the volume of BG particles in the biopsy decreased from 29% at 4 months to 15% at 6 months and 8% at 15 months. The BG particles appeared to resorb within 1-2 years by dissolution rather than by osteoclastic activity. Parameters for bone turnover (% osteoid surface, % resorption surface) indicated that bone remodeling was very active at both experimental and control sides, during more than 6 months. These results suggest that mixtures of mainly (80-90%) BG particles and some (10-20%) autogenous bone are effective for bone regeneration in the augmented sinus offer 6 months healing time, while about 12 months healing time is needed for 100% BG particles.

Surface transformation of bioactive glass in bioreactors simulating microgravity conditions. Part I: experimental study

Surface modified bioactive glass with surface properties akin to those of the bone mineral phase is an attractive candidate for use as a microcarrier material for 3-D growth of bone-like tissue in rotating wall vessel bioreactors (RWVs). The critical surface properties of this material are the result of reaction in solution. Because an RWV environment is completely different from conditions previously employed for bioactive glass testing, a detailed study of the surface reactions is warranted. Under properly chosen conditions, RWVs can also provide a simulated microgravity environment for the bioactive glass (BG) particles. In this sense, this study is also a report on the behavior of a bioactive material under microgravity conditions simulated on earth. A high aspect ratio vessel (HARV) and carefully selected experimental conditions enabled the simulation of microgravity in our laboratory. A complimentary numerical study was simultaneously conducted to ascertain the appropriateness of the experimental parameters (particle size, particle density, medium density, medium viscosity, and rotational speed) that ensure simulated microgravity conditions for the glass particles in the HARV. Physiological solutions (pH 7.4) with and without electrolytes, and also with serum proteins, were used to study the change in surface character resulting from simulated microgravity. Control tests at normal gravity, both static and dynamic, were also conducted. Solution and surface analyses revealed major effects of simulated microgravity. The rates of leaching of constituent ions (Si-, Ca-, and P-ions) were greatly increased in all solutions tested. The enhanced dissolution was followed by the enhanced formation of bone-like minerals at the BG surface. This enhancement is expected to affect adsorption of serum proteins and attachment molecules, which, in turn, may favorably affect bone cell adhesion and function. The findings of the study are important for the use of bioactive materials as microcarriers to generate and analyze 3-D bone-like tissue structures in bioreactors under microgravity conditions or otherwise.

Surface transformation of bioactive glass in bioreactors simulating microgravity conditions. Part II: numerical simulations

The effects of simulated microgravity on the surface modification of bioactive glass (BG) in solution were studied using a numerical method. Models were developed for estimating the mass transfers of different chemical species from the surface of bioactive glass particles (microcarriers) suspended in the rotating liquid medium of a NASA-designed high aspect ratio vessel (HARV) bioreactor and on the bottom surface of a static vial. The concentration profiles resulting from chemical reactions and ionic transports were ascertained. Numerical results for the transport under simulated microgravity in the HARV and at normal gravity in the static vial were compared. These results were also compared with those of experiments to verify the enhancement of the reaction kinetics under simulated microgravity conditions. The experimental and numerical studies confirm that simulated microgravity conditions lead to the quick achievement of bioactive glass surface modification.

In vitro transformation of bioactive glass granules into Ca-P shells

Bioactive glass (BG) granules of narrow size are excavated when implanted in mandibular bone of beagles. Bone tissue forms within these internally hollowed particles without a connection to the bone at the margins of the defect. In this study the internal excavation of BG granules was simulated by in vitro immersion experiments. Postimmersion solutions were analyzed for changes in Si, Ca, and P concentrations. Using scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and Fourier Transform Infrared (FTIR) spectroscopy, granules were analyzed for compositional, morphologic, and structural changes resulting from immersion. Only when the solution was continuously replenished and only if this solution was composed of electrolyte- and protein-containing serum was excavation achieved. Without solution replenishment, that is, under so-called integral immersion conditions, the solution quickly became saturated in silicon, and the silicon no longer dissolved. When the glass was immersed in a solution with serum, a porous surface structure with fine precipitates was formed, in contrast to a dense surface reaction layer with closely packed globular precipitates that was formed in a solution without serum. The combined effect of continuous solution replenishment and the use of a solution containing serum proteins led to the formation of a surface reaction layer that did not impede continued corrosion. As such, all Si was released, and eventually a hollow Ca-P shell was formed. Thus this study supports the hypothesis that there is a physico-chemical mechanism of Si transport through the Ca-P-rich layer followed by Si dissolution. This mechanism may be operative in vivo and thereby may contribute to the observed in vivo excavation.

Bioactive ceramics: the effect of surface reactivity on bone formation and bone cell function

Surface reactivity is one of the common characteristics of bone bioactive ceramics. It contributes to their bone bonding ability and their enhancing effect on bone tissue formation. During implantation, reactions occur at the material-tissue interface that lead to time-dependent changes in the surface characteristics of the implant material and the tissues at the interface. This review describes some of the current concepts regarding the surface reactivity of bone bioactive materials and its effect on attachment, proliferation, differentiation and mineralization of bone cells.

Biocompatibility of glass-crystalline materials obtained by the sol-gel method: effect on macrophage function

The aim of this work was to confirm in vitro biocompatibility of a new gel-derived glass-crystalline material containing hydroxyapatite and wollastonite phases. For the purpose of comparison, studies were also carried out for a material of the same chemical composition obtained by the traditional melting method. We examined the behaviour and response of cells cultured in the presence of the studied materials. The level of activation of macrophages in culture was determined using three different methods: measurement of respiratory burst by chemiluminescence, nitrite assay and by bioassay of secreted cytokines after immunoelectrophoresis of acute phase proteins from hepatoma cells. All our results show a relatively low, close to control level, activation of macrophages exposed to the studied materials. This indicates a good biocompatibility of both the gel-derived material and the material obtained by the traditional melting method.